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Chapter 13: Plant Growth and Development

Grade 11 Science | Chapter 13

Plant Growth and Development

Plants grow throughout their lives. This chapter develops growth and its phases, where growth happens, the plant hormones that control it, and how plants respond to their surroundings.

Core Concepts

Key Principles

Worked Examples

Practice Sets

Contents

Introduction: Growth and Development

The Phases of Growth

Where Growth Happens

Plant Hormones

Responses to Stimuli (Tropisms)

Development and Differentiation

Key Reasoning (Principles)

Worked Examples (10)

Practice Sets A to D

10.

Summary and Exam Quick-Check

1. Introduction: Growth and Development

Unlike most animals, plants grow throughout their lives. Growth is a permanent increase in size, while development is the whole sequence of changes from a seed to a mature plant. This chapter looks at how growth proceeds, where in the plant it occurs, and the hormones and signals that guide it.

Core idea

Plants grow at meristems in a typical S-shaped pattern. Hormones coordinate growth and development, and plants respond to light, gravity and other stimuli by directed growth called tropisms.

2. The Phases of Growth

When growth is measured over time it follows a typical S-shaped curve with three phases. In the lag phase growth is slow as the plant prepares. In the rapid or log phase growth is fast as cells divide and enlarge. In the stationary phase growth slows and levels off as the plant matures. The same pattern appears in a single organ or a whole plant.

Diagram 1 – The Growth Curve

An S-shaped growth curve with lag, rapid and stationary phases

Fig 1. Growth is slow at first, then rapid, then levels off, giving an S-shaped curve.

3. Where Growth Happens

Growth is concentrated in regions of dividing cells called meristems, found at the tips of roots and shoots. Just behind the protective root cap lies the zone of cell division, then the zone of elongation where cells lengthen, and then the zone of maturation where cells specialise and root hairs appear. So a root grows mainly at its tip.

Diagram 2 – Regions of a Growing Root

The zones of cell division, elongation and maturation in a root tip

Fig 2. A root grows in zones, from the dividing cells behind the cap, through elongation, to maturation.

4. Plant Hormones

Growth is coordinated by chemical signals called plant hormones. Auxin drives cell growth and the bending of a shoot toward light. Gibberellins promote stem growth and seed germination. Cytokinins promote cell division. Abscisic acid brings on dormancy and closes the leaf pores in dry conditions, while ethylene ripens fruit. Together they balance growth against the conditions.

Diagram 3 – Plant Hormones

The plant hormones auxin, gibberellin, cytokinin, abscisic acid and ethylene with their roles

Fig 3. The main plant hormones and the growth processes they control.

5. Responses to Stimuli (Tropisms)

Plants cannot move, but they respond to their surroundings by directed growth called a tropism. In phototropism a shoot grows toward light, because auxin gathers on the shaded side and makes it grow faster, bending the shoot. In gravitropism roots grow downward and shoots upward in response to gravity. These responses help the plant reach light, water and support.

6. Development and Differentiation

Beyond simply getting bigger, a plant develops: its cells differentiate into the many specialised types, and organs form in the right places at the right times. The same set of genes can give rise to a root cell or a leaf cell depending on signals. Development also includes events such as flowering, which many plants time by the length of day and night.

7. Key Reasoning (Principles)

Principle 1: Growth is concentrated at meristems

Because only meristematic cells divide, growth happens mainly at the tips of roots and shoots, and a root lengthens just behind its cap.

Principle 2: Hormones coordinate growth

Chemical signals such as auxin, gibberellins and cytokinins control where and how fast the plant grows, balancing growth against the conditions.

Principle 3: Directed growth lets a fixed plant respond

Through tropisms a plant grows toward or away from a stimulus such as light or gravity, so even without moving it can reach what it needs.

8. Worked Examples

Example 1

Q: What is the difference between growth and development?

▶ Show Solution

Growth is an increase in size; development is the whole sequence of changes from seed to mature plant.

Answer: Size versus the whole change.

Example 2

Q: What shape is the typical growth curve?

▶ Show Solution

An S shape.

Answer: An S shape.

Example 3

Q: Name the three phases of growth.

▶ Show Solution

Lag, rapid (log) and stationary.

Answer: Lag, rapid, stationary.

Example 4

Q: Where is growth concentrated in a plant?

▶ Show Solution

At the meristems, at the tips of roots and shoots.

Answer: At the meristems.

Example 5

Q: Name the zones of a growing root from the tip.

▶ Show Solution

Root cap, cell division, elongation and maturation.

Answer: Cap, division, elongation, maturation.

Example 6

Q: Which hormone makes a shoot bend toward light?

▶ Show Solution

Auxin.

Answer: Auxin.

Example 7

Q: Which hormone ripens fruit?

▶ Show Solution

Ethylene.

Answer: Ethylene.

Example 8

Q: What is a tropism?

▶ Show Solution

A directed growth response of a plant to a stimulus.

Answer: A directed growth response.

Example 9

Q: In which direction do roots grow in response to gravity?

▶ Show Solution

Downward.

Answer: Downward.

Example 10

Q: What is differentiation?

▶ Show Solution

The process by which cells become specialised for particular jobs.

Answer: Cells becoming specialised.

9. Practice Sets A to D

Set A – Multiple Choice (Basic)

1. The growth curve is shaped like the letter: (a) V (b) S (c) L (d) T

2. Growth is concentrated at the: (a) leaves (b) meristems (c) flowers (d) bark

3. The hormone that bends a shoot to light is: (a) ethylene (b) auxin (c) cytokinin (d) abscisic acid

4. Fruit ripening is promoted by: (a) auxin (b) ethylene (c) gibberellin (d) cytokinin

5. A root growing downward shows: (a) phototropism (b) gravitropism (c) dormancy (d) ripening

▶ Reveal Answers

1. (b) S.

2. (b) meristems.

3. (b) auxin.

4. (b) ethylene.

5. (b) gravitropism.

Set B – Short Answer (Understanding)

1. Define growth and development.

2. Name the three phases of the growth curve.

3. List the zones of a growing root.

4. Name three plant hormones and a role of each.

5. What is a tropism?

▶ Reveal Answers

1. Growth is a permanent increase in size; development is the full sequence of changes from seed to mature plant.

2. Lag, rapid (log) and stationary.

3. Root cap, zone of cell division, zone of elongation and zone of maturation.

4. Auxin (growth and bending to light), gibberellin (stem growth and germination), cytokinin (cell division).

5. A directed growth response to a stimulus such as light or gravity.

Set C – Application and Reasoning

1. A shoot on a windowsill bends toward the window. Name the response.

2. Which hormone causes that bending?

3. Where does a root grow fastest?

4. Which hormone helps a plant survive drought, and how?

5. Why does a seedling root grow downward?

▶ Reveal Answers

1. Phototropism.

2. Auxin.

3. Just behind the tip, in the zones of division and elongation.

4. Abscisic acid, which closes the leaf pores to reduce water loss.

5. Because of gravitropism, the directed growth response to gravity.

Set D – Higher Order (Challenge)

1. Explain how auxin causes a shoot to bend toward light.

2. Explain why the growth curve levels off in the stationary phase.

3. Explain why growth being at meristems means a tree gets taller only at its tips.

4. Explain how a plant, though fixed, can still reach light and water.

5. Explain how the same genes can make different cell types.

▶ Reveal Answers

1. Auxin gathers on the shaded side of the shoot and makes those cells grow longer, so that side lengthens more and the shoot bends toward the light.

2. Because the plant or organ approaches its mature size and cell division and enlargement slow down.

3. Because the dividing cells are at the shoot tips, so new length is added there, while older parts do not lengthen.

4. Through tropisms, growing toward light and downward toward water, it positions itself without moving.

5. Signals switch different genes on or off in different places, so cells differentiate into roots, leaves or other types.

Chapter Summary

Growth and Development

Growth is increase in size; development is the whole change.

Growth Curve

S shaped: lag, rapid and stationary phases.

Meristems

Growth is concentrated at root and shoot tips.

Root Zones

Cap, division, elongation, maturation.

Hormones

Auxin, gibberellin, cytokinin, abscisic acid, ethylene.

Tropisms

Directed growth toward light (photo) or with gravity (gravi).

Quantity

Unit

Symbol

Growth curve

S shaped

–

Growth site

meristems

–

Bending hormone

auxin

–

8-Point Exam Quick-Check

Growth is increase in size; development is the whole sequence of change.

The growth curve is S shaped: lag, rapid, stationary.

Growth is concentrated at meristems in root and shoot tips.

Root zones: cap, cell division, elongation, maturation.

Hormones: auxin, gibberellin, cytokinin, abscisic acid, ethylene.

Auxin bends a shoot toward light by gathering on the shaded side.

Tropisms are directed growth responses to light and gravity.

Differentiation makes cells specialise for their jobs.

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Class 11 Biology Chapter 13: Plant Growth and Development, Complete Notes and Practice

This revision guide follows the current NCERT Class 11 Biology syllabus and develops plant growth, covering growth and development, the S-shaped growth curve with its lag, rapid and stationary phases, the meristems and zones of a growing root, the plant hormones such as auxin, gibberellin, cytokinin, abscisic acid and ethylene, and the directed growth responses called tropisms, with three diagrams, ten worked examples and graded practice. Visit SchoolRevise.com to revise, practise and excel.